Muffler with concentric tubes forming helmholtz chambers



R. A. HEATH Nov. 21, 1967 MUFFLER WITH CONCENTRIC TUBES FORMINGHELMHOLTZ CHAMBERS 2 Sheets-Sheet l NVENTOR.

P J N Q Filed Feb. 16, 1965 R. A. HEATH 3,353,627

MUFFLER WITH CONCENTRIC TUBES FORMING HELMHOLTZ CHAMBERS Nov. 21, 1967 2Sheets-Sheet 2 Filed Feb. 16, 1965 INVENTOR. /7. H64 2 BY jam,

w Z an/vzns United States Iatent Gfilice 3,353,627 MUFFLER WITHCONCENTRIC TUBES FORMING HELMHQLTZ CHAMBERS Robert A.'Heatl1, Jackson,Mich, assignor to Walker Manufacturing Company, Racine, Wis., acorporation of Delaware Filed'Feb. 16, 1965, Ser. No. 433,225 13 Claims.(Cl. 181-48) My invention relates to mufilers and is particularly,though not exclusively, concerned with mufiiers of the type that areused in exhaust systems for internal combustion engines such as arefound in automobiles and trucks.

It is an object of my invention to provide a muffler structure whichincorporates various silencing principles but which is small indiameter, contains a minimum number of parts, and is economical toproduce.

The invention accomplishes the foregoing and other objects by means of aconstruction in which there is a center tube that serves as a gasconveying conduit and it. is surrounded by an outer tube which may alsoform the outer housing or shell of the muffler. Between the two tubes isan inner shell which is preferably held in place by means of pinchedsections formed on either the outer tube togrip the shell or on theshell to grip the center tube. The space between the intermediate shelland either-the outer tube or the center tube, or both, forms a passagewhich is used as a tuning neck to lead into a chamber formed between thecenter tube and the outer tube and act with the chamber as a Helmholtzresonator to'attenuate desired frequencies.

The invention is illustrated in the accompanying drawings in which: 1

FIGURE 1 is a longitudinal cross section, partly broken away, throughone form of the invention;

FIG. 2 is a cross-sectional along the line 22 of FIG. 1; FIG. 3 is alongitudinal cross-section through another form of the invention;

FIG. 4 is a cross section on the line 4-4 of FIG. 3;

FIG. 5 is a longitudinal section, partly broken away, through anotherform of the invention;

FIG. 6 is a longitudinal cross section, partly broken away, through afourth form of the invention; and

FIG. 7 is a cross section along the line 77 of FIG. 6.

The muffler 1 of FIGS. 1 and 2 comprises a center tube 3' which issupported at opposite ends in the reduced diameter portions 5 and 7,which form the inlet and outlet bushings of the muffler 1. The bushings5 and 7 may be formed by swaging down the ends of the outer tube 9 whichforms the outer shell of the housing of the mufiler 1. Adjacent theinlet end of the muffler 1 the tube 3' is preferably providedwith a bankof louvers or perforations ll .whichfopen into the space between thecenter tube 3 and the outer tube 9. Surrounding the center tube, locatedat an intermediate point of its length,

is an inner shell 13. At its upstream end the shell is supported by apinched or rolled-down section formed in the outer tube 9 which providesa gas-tight fit with theperiphery of the shell 13. This, therefore,divides the space within the outer tube 9 into'a first chamber 17 whichis in direct communication with the louvers 11, and a second chamber 19which surrounds and is located downstream of the shell 13. The chamber19 has communication withthe 'gas in the chamber 17 by means of thepinch-down connection 21 between the downstream end of the shell 13 inthe center tube 3, which is of such a nature as to leave open passages23 which provide a large open area communicating the interior of theshell 13 with the chamber 19. It will be seen that the shell 13 and thecenter tube 3, in effect, define an annular pas- 3,353,027 Patented Nov.21, 1967 sage 25 which is open at 23 or its downstream end into thechamber 19 and at 27 or its upstream end into the chamber 17. Ifdesired, the shell 13 may overlap a portion of the bank of louvers 11,as indicated in FIG. 1. It will be seen that that portion of the annularpassage 25 between the downstream end of the bank of louvers and thedownstream end of the shell 13, i.e., the distance L in the drawings,constitutes a tuning neck or throat which will act in conjunction withthe volume of chamber 19 to provide a Helmholtz resonator which willattenuate frequencies to which it is tuned. The natural frequency ofthis resonator is capable of being calculated by the well-knownHelmholtz formula, the frequency being dependent upon the volume ofchamber 19, the length of the passage 25, and the area of the passage25.

That portion of the passage 25 which overlaps a portion of the louverbank is indicated at 29 and will serve to some eXtent as a highfrequency sound attenuating chamber to attenuate spit and scratchinessand high frequency noises, whereas the chamber 17 will also attenuatethese sounds as well as lower frequency sounds and roughness. Since thegas and sound in chamber 17 has communication with the chamber 19 onlythrough the annular passage 25, which passage includes the length Lwhich is imperforate, lower-frequency sounds or notes of the frequencyto which this structure is tuned will be attenuated.

In the embodiment 101 of FIGS. 3 and 4 there is a center tube 103 whichis received in the reduced diameter end sections 105 and 107 of theouter tube 109, the sections 105 and 107 forming inlet and outletbushings, respectively, for the muflier 101. The center tube 103 isprovided with two banks of louvers or perforations 111 and 113.Surrounding the bank 113 is an intermediate shell 115 which has gas-typeconnections 117 and 119 at opposite ends with the center tube, thesebeing illustrated in FIG. 4 as formed by pinched-down sections 121 inthe end of the shell 115. The shell therefore defines a spit chamber 123with the center tube 103 into which high frequency sounds pass from thelouver bank 113 and are attenuated. The outer periphery of the shell 115defines an annular passage 125 with the outer tube 109. The upstream endof the annular passage 125 is open as seen at 127 to communicate freelywith a chamber formed between the center tube 103 and the outer tube 109and located between the open end 127 and the upstream end of the.mufiier. The downstream end of the annular passage 125 is open, asindicated at 131, and in free communication with a chamber. 133 that isformed in the mufiler between the center tube and the outer tube andlocated downstream in the open end 131.

The passage 125 is of a length and an area that are selected inrelationship withthe volume of chamber 133 to provide a Helmholtzresonator that is-tuned to attenuate a desired frequency.

As already indicated, the spit chamber 123 will at.- tenuate scratchynoises and high frequency hissing sounds.

The chamber 129 will act to eliminate somewhat lower frequencies androughness and, if desired, the length of the chamber 129 may be selectedwith respect to the center of the bank of louvers 111 so that it isapproximately one-quarter of the wave length of any frequency which itisdesired to attenuate.

Thus, the unit 101 with only three parts has at least four differentsilencing techniques embodied in it, namely: 1) spit chamber for highfrequencies, (2) the Helmholtz resonator, (3) the roughness controlchamber 129 and (4) a'quarter wave length tuner or quincke tube.

It will be understood that the quarter wave length tuning techniquecould be applied to other embodiments of the invention, including thoseillustrated herein if desired.

The mufiler 201 of FIG. 5 has a center tube 203 which is supported inthe reduced diameter sections 205 and 207, which form inlet and outletbushings, respectively, for the outer tube 209. The center tube 203 hasa bank of louvers 211 and a second bank of louvers 213 locateddownstream of the louvers 211. Surrounding the bank of louvers 213 andextending downstream a substantial distance beyond the end of the bank213 is a shell 215. The upstream end of the shell 215 is connected tothe center tube 203 in a gas-tight joint 217 by necking down, rolling,swaging, or pinching down the upstream end of the shell 215. Thedownstream end of the shell 215 is open, as indicated at 219, for freecommunication with a chamber 221 which is formed by the center tube 203and the outer tube 209 and which extends from the downstream end 223 ofthe outer tube to the shell 215. While the downstream end of the shell215 is shown as unsupported on the center tube, it is obvious that itcould be supported by the technique shown in FIG. 2 if that is desired.A length L of the center tube inside of the shell 215 is imperforate sothat the shell and the center tube define-an annular passage 225 whichwill serve as a tuning neck of the chamber 221. The annular space 227between the shell 215 and the center tube 203 located immediatelyupstream of the passage 225 will form a modified spit chamber, and alsoserves to deliver gases and sound waves to the passage 225.

The outer periphery of the shell 215 and the inner periphery of the tube209- define an annular passage 229 which is substantially longer thanthe passage 225 as well as being of larger cross-sectional area in theparticular embodiment shown since it is of larger diameter andapproximately the same width. The passage 229 will communicate thechamber 231 which is formed between the center tube 203 and the outertube 209 and located upstream of the shell 215 with the chamber 221, andsound waves being delivered to the chamber 231 by the bank of louvers211. Thus, in this embodiment the chamber 221 is connected through twodifferent tuning necks to the gas flowing through the center tube 203,that is, the tuning neck provided by annular passage 225 and the tuningneck provided by the annular passage 229, both of which are formed bythe inner shell 215'. Assuming the areas of the passages 225 and 229 arethe same, it will be seen that the passage 229 acting in conjunction.with the chamber 221, will form a Helmholtz resonator having afundamental frequency which is substantially higher than that formed bythe passage 225 in the chamber 221 inasmuch as the frequency isinversely proportional to the square root of the length of the tuningpassage.

The chamber 231 will act to attenuate roughness and spit noises as wellas serve as a feeder chamber, or collection chamber, for furnishingpressure to the annular passage 229, all as in the precedingembodiments.

Additionally, the length of the outer tube 209 downstream from about themidpoint of the bank of louvers 211 may be such as to serve as a quarterwave length tuning chamber for an objectionable frequency. In this case,the chamber 221 would serve as a portion of two different Helmholtzresonators and also as a portion of a quincke or quarter wave lengthtuning chamber.

The muffler 301 of FIGS. 6 and 7 has a center tube 303 which issupported in reduced diameter sections 305 and 307 which form inlet andoutlet bushings, respectively, for the outer tube 309. The center tubehas three banks of perforations .or louvers 311-, 3:13, and 315,respectively,

formed in it. Surrounding the upstream and the downstream bank oflouvers are'inner shells 317 and 3159, respectively, which have theopposite. ends pinched down, as indicated at 321, by pinches 323, intogas tight connections at opposite ends with the center tube 303. Thus,there is a spit chamber 325 formed by the shell 317 and ,a spit chamber327 formed by the shell 319. The shells 317 and 3 19 may, of course, .beof .dilferent lengths to form chambers of different volumes, if desired.It is clear that the louvers 311 and 315 opening into the chambers 325and 327 act to attenuate high frequency noises and spit.

The outer diameter of the shells 317 and 319 define annular passages 329and 331, respectively, with the er ube 0.9 whi h are in op n ommuniction at the upstream end 333 of the passage 3.29 and the downstream end335 of the passage 331 with the chambers 337 and 339, respectively. Thedownstream end 3.41 of the passage 329 and the upstream end 343 of theannular passage 331 are in open communication with a chamber 345 whichis defined by the center tube 303 and the outer tube 309 into which thebank of louvers 313 opens. The chamber 345 will attenuate roughness andserve as a collection or feeder chamber for the passages 329 and 331. Itis clear that by making the volumes of chambers 337 and339- of such sizein relation to the respective lengths and areas of the passages 329 and331 that two substantially differently tuned Helmholtz resonators can beobtained in the muffler 301.

It will now be recognized that by the use of a center tube, an outertube, and an intermediate shell the invention provides various possiblemuffler constructions capable of silencing sounds of high, low, andintermediate frequencies by means of various silencing techniques.Modifications in the specific structures shown may be made withoutdeparting from the spirit and scope of the invention.

I claim:

7 1. A gas mufiler for attenuating sound of a predetermined frequencycomprising an outer tube, an inner center tube, and an intermediateshell telescoped between said tubes, at least part of the space betweensaid tubes form-mg a chamber of predetermined volume having a majorportion located out of radial alignment with said shell, at least onecross section of said shell being connected in a gas tight joint to oneof said tubes, said shell forming with the other of said tubes anannular passage of predetermined length and area and having first andsecond ends and both said ends being open, the first end of said passageopening to said predetermined volume chamber, said center tube formingthe gas flow passage for saidmufilenthe length and area of said annularpassage and the volume of said chamber being interrelated and selectedto form a Helmholtz sound attenuating chamber for-said predeterminedfrequency, and means forming a flow connection of said gas flow passagewith the second end of said annular passage.

2,. A rnufiler as defined in claim 1 wherein said gas tight joint isbetween said outer tube and said shell whereby said annular passage isformed by said shell and said center tube, said joint subdividing thespace between said tubes into said chamber of predetermined volume andinto a second chamber, said means and said second end .both opening intosaid second chamber.

3. A muffler as, defined in claim 2 wherein said means comprisesperforations in the center tube and said second chamber acts toattenuate roughness sound in the gas.

4. A mufller as defined in claim '1 wherein said gas tight joint isbetween said center tube and said shell whereby said annular passage isformed by said shell and said outer tube.

5. A muffier as defined in claim 4 wherein a chamber is formed betweensaid tubes adjacent the second end of said annular passage, said meanscomprising perforations in said center tube opening into saidjust-mentioned chamber. j

6. A mufiler as defined in claim 5 wherein longitudinally spaced gastight joints are formed between. said shell and center tube to provide achamber between the cen er tube and shell, said center tube. beingperforated within said last-mentioned chamber. 7

7. A mufiler as defined in claim 1 wherein longitudi nally spaced gastight joints are formed between said shell and center tube to provide achamber between the center tube and shell, said center tube beingperforated within said last-mentioned chamber.

8. A mufiier as defined in claim 1 wherein said gas tight joint isbetween said center tube and said shell whereby said annular passage isformed by said shell and said outer tube, said shell and said centertube defining an annular passage opening at one end of the shell intothe space between the tubes, a portion of said tube located inwardly ofthe open end of the annular passage formed between said shell and centertube being perforate, the area of said last-mentioned annular passageand the imperforate length thereof and the volume of the space intowhich it opens being selected to form a Helmholtz sound attenuatingchamber for a desired frequency.

9. A mufi ler as defined in claim 8 wherein said two annular passagesboth open into the same chamber and are tuned to attenuate two differentfrequencies.

10. A mufiler as defined in claim 9 wherein the center tube in the spacebetween said tubes adjacent the second end of said annular passage isperforated whereby such space acts as a roughness sound attenuatingchamberv 11. A mufiler as claimed in claim'l including a secondintermediate shell telescoped between said tubes and spacedlongitudinally of the other shell, a pair of gas tight joints connectingeach shell to the center tube to form a spit chamber between each shelland the center tube, said center tube being perforated in each spitchamber and also being perforated between the two shells to open intothe space between the tubes intermediate the two shells, said two shellsand said outer tube defining two annular passages having second endsopening into said intermediate space, the two spaces between the tubesadjacent the two first ends of the annular passages being ofpredetermined volumes and respectively related to the lengths and areasof the annular passages to act as tuning chambers.

12. A mufiler as claimed in claim 11 wherein said two annular passagesand the two spaces are tuned to attenuate two ditferent frequencies.

13. A mufiier as claimed in claim 1 wherein the length of the spacebetween said tubes communicating with said means is substantially onequarter the Wave length of a selected frequency to be attenuated.

References Cited UNITED STATES PATENTS 2,124,933 7/1938 Starkweather18148 2,139,151 12/1938 Deremer 18148 2,297,046 9/1942 Bourne 181-482,331,344 10/1943 Powers 181-48 X 2,367,753 1/1945 Buck. 2,580,5641/1952 Ludlow l814-8 2,899,007 8/1959 Morrish et a1. 18154 2,930,4403/1950 Fetzer et al. 181-54 3,263,772 8/1966 Irwin et al. 18l-59 FOREIGNPATENTS 450,398 7/ 1936 Great Britain. 258,890 6/1928 Italy.

RICHARD B. WILKINSON, Primary Examiner. ROBERT S. WARD, JR., AssistantExaminer.

1. A GAS MUFFLER FOR ATTENUATING SOUND OF A PREDETERMINED FREQUENCYCOMPRISING AN OUTER TUBE, AN INNER CENTER TUBE, AND AN INTERMEDIATESHELL TELESCOPED BETWEEN SAID TUBES, AT LEAST PART OF THE SPACE BETWEENSAID TUBES FORMING A CHAMBER OF PREDETERMINED VOLUME HAVING A MAJORPORTION LOCATED OUT OF RADIAL ALIGNMENT WITH SAID SHELL, AT LEAST ONECROSS SECTION OF SAID SHELL BEING CONNECTED IN A GAS TIGHT JOINT TO ONEOF SAID TUBES, SAID SHELL FORMING WITH THE OTHER OF SAID TUBES ANANNULAR PASSAGE OF PREDETERMINED LENGTH AND AREA AND HAVING FIRST ANDSECOND ENDS AND BOTH SAID ENDS BEING OPEN, THE FIRST END OF SAID PASSAGEOPENING TO SAID PREDETERMINED VOLUME CHAMBER, SAID CENTER TUBE FORFORMING THE GAS FLOW PASSAGE FOR SAID MUFFLER, THE LENGTH AND AREA OFSAID ANNULAR PASSAGE AND THE VOLUME OF SAID CHAMBER BEING INTERRELATEDAND SELECTED TO FORM A HELMHOLTZ SOUND ATTENUATING CHAMBER FOR SAIDPREDETERMINED FREQUENCY, AND MEANS FORMING A FLOW CONNECTION OF SAID GASPASSAGE WITH THE SECOND END OF SAID ANNULAR PASSAGE.